1. Field of the Invention
The present invention relates to a subchannel and power allocation method, an apparatus using the same, and a transmitting apparatus of a communication system.
2. Description of the Related Art
An Orthogonal Frequency Division Multiplexing (OFDM) method applied to a communication system divides a frequency bandwidth into a plurality of sub-frequency bandwidths (i.e., subchannels) and simultaneously transmits data through the subchannels. An Orthogonal Frequency Division Multiple Access (OFDMA) method is a multi-user version of the OFDM. In an OFDMA-based communication system, a scheduler of a base station allocates a subchannel to a user equipment (UE) according to a channel state of the user so as to satisfy service requirements of the UE. In this case, the scheduler determines a modulation coding scheme for each subchannel and allocates a subchannel so as to satisfy a transmission bit rate of the UE.
According to a subchannel allocation method for a conventional communication system, a transmitter of a base station determines a modulation/demodulation coding scheme based on a Signal to Noise Ratio (SNR) of a receiver of a terminal. A modulation/demodulation coding algorithm proposed by J. Campello sends channel information of all subcarriers as feedback and selects an appropriate modulation algorithm for each subcarrier for achieving optimum performance.
However, according to the algorithm proposed by J. Campello, an appropriate modulation/demodulation algorithm for each subcarrier is determined by allocating one transmission bit through one calculation, and this process is repeated to allocate transmission bits to the overall subcarriers. Such an algorithm that allocates bits by repeating the above process can be applied without any difficulty when the number of UEs is small, but it may be complicated when the number of UEs is large. In addition, such an algorithm uses a received SNR as feedback information, and accordingly, an accurate received SNR is required for providing appropriate performance, thereby causing an increase of the amount of feedback information.